1. Field of the Invention
The present invention relates to a method of driving a matrix-display-type display panel.
2. Description of the Related Art
In recent years, plasma display devices having an AC (AC discharge) type plasma display panel (hereinafter, referred to as PDP), which is a small-sized display panel, mounted thereon, have been produced (see, for example, Japanese Patent Kokai No. 2003-22045 (hereinafter, referred to as Patent Document 1).
In a PDP, a display cell having a discharge space is formed at each of the intersections of a plurality of column electrodes and a plurality of row electrodes. The plurality of column electrodes are disposed to extend in a longitudinal direction (vertical direction) of a two-dimensional display screen, and the plurality of row electrodes are disposed to extend in a transverse direction (horizontal direction). A plasma display device selectively discharges display cells by applying various driving pulses to the column electrodes and the row electrodes of the PDP, and forms display images on a screen by light emission through the discharge. At this time, since each of the display cells emits light using a discharge phenomenon, it emits light with the highest luminance or does not emit light. That is, each of the display cells can express only two luminance levels corresponding two grayscales. Thus, grayscale drive based on a subfield method is performed to realize intermediate luminance display according to an input video signal in the PDP having the display cells.
In the grayscale drive based on a subfield method, a display period of an image corresponding to one field or one frame is divided into N subfields. A light emission period (the number of times of light emission) corresponding to the weight of each of bits of the pixel data (N bits) is allocated to each subfield, and the light emission drive for the PDP is performed.
For example, when one field is divided into six subfields SF1 to SF6, the following light emission periods are respectively allocated to the subfields (see FIG. 1 of Patent Document 1).
SF1: 1
SF2: 2
SF3: 4
SF4: 8
SF5: 16
SF6: 32
According to luminance levels expressed by an input video signal, light emission is selectively performed in each of the subfields SF1 to SF6. In this process, the intermediate luminance corresponding to the sum of the light emission periods performed during one field period (SF1 to SF6) is viewed. For example, when a display cell emits light in only the subfield SF6 of the subfields SF1 to SF6, the display cell emits light only for a period corresponding to “32” in one field. Therefore, an intermediate luminance corresponding to “32” is viewed. In the meantime, when a display cell emits light in each of the subfields SF1 to SF5, except for the subfield SF6, the display cell emits light for a period corresponding to “31” (=“1”+“2”+“4”+“8”+“16”) in one field. Therefore, an intermediate luminance corresponding to “31” is viewed.
In this case, with the six subfields, 64 combinations (light emission patterns) of subfields to emit light and subfields not to emit light are obtained. With the 64 light emission patterns, 64 combinations of light emission periods in one field are obtained. Therefore, it is possible to express intermediate luminance corresponding to each of 64 grayscales.
Here, for example, in one field, a light emission period and a blackout period of a display cell G31 corresponding to a pixel for expressing luminance “32” are reverse to those of a display cell G32 corresponding to a pixel for expressing luminance “31” (see FIG. 1 of Patent Document 1). Therefore, in a case of seeing the screen of the PDP, if one sees the display cell G32 in periods of SF1 to SF5 and then moves the sight to the display cell G31 as shown by a broken line in FIG. 1, one continuously sees only the blackout periods of both of them. As a result, a dark line is viewed on a boundary between them as a false contour, thereby degrading the image quality.
Further, a driving method was proposed in which a display cell lights in the continuous subfields the number of times corresponding to luminance to be express and then maintains a blackout state until reaching the subfield SF6 (see FIG. 2 of Patent Document 1). According to this driving method, light emission patterns whose relationships between a light emission period and a blackout period are reverse to each other in one filed do not exist. Therefore, the above-mentioned false contour is not generated.
However, when a driving pulse for generating the discharge is applied to one of adjacent display cells and is not applied to the other, since these display cells suffer interference of an electric field from each other, some cases where discharge is not correctly generated occur. In order to prevent such a case from occurring, according to the above-mentioned driving method, even a display cell once shifted to a blackout state is repeatedly supplied with a driving pulse for generating discharge to shift the display cell to the blackout state. For this reason, there has been a problem that the power consumption is relatively high even at the time of low luminance display.